<p>A regex should never include a repetitive pattern whose body would match the empty string. This is usually a sign that a part of the regex is
redundant or does not do what the author intended.</p>
<h2>Noncompliant Code Example</h2>
<pre>
"(?:)*"      // same as the empty regex, the '*' accomplishes nothing
"(?:|x)*"    // same as the empty regex, the alternative has no effect
"(?:x|)*"    // same as 'x*', the empty alternative has no effect
"(?:x*|y*)*" // same as 'x*', the first alternative would always match, y* is never tried
"(?:x?)*"    // same as 'x*'
"(?:x?)+"    // same as 'x*'
</pre>
<h2>Compliant Solution</h2>
<pre>
"x*"
</pre>

